Mode d’emploi
- Copiez la commande et examinez le paquet avant de l’installer dans votre environnement agent.
- Consultez le document original pour les outils, identifiants et environnements requis.
- Décrivez les entrées et le livrable souhaité ; comparez la sortie aux sources.
npx skills add https://github.com/actionbook/rust-skills --skill m06-error-handlingAvant de commencer
- L’installation n’inclut ni abonnement au modèle, ni quota API, ni accès aux fichiers.
- Étoiles et installations reflètent l’activité, pas un test indépendant de qualité ou de sécurité.
Document Skill original
Rendu depuis le dépôt source en conservant titres, exemples, code, tableaux, liens et images.
Error Handling
Layer 1: Language Mechanics
Core Question
Is this failure expected or a bug?
Before choosing error handling strategy:
- Can this fail in normal operation?
- Who should handle this failure?
- What context does the caller need?
Error → Design Question
| Pattern | Don't Just Say | Ask Instead |
|---|---|---|
| unwrap panics | "Use ?" | Is None/Err actually possible here? |
| Type mismatch on ? | "Use anyhow" | Are error types designed correctly? |
| Lost error context | "Add .context()" | What does the caller need to know? |
| Too many error variants | "Use Box<dyn Error>" | Is error granularity right? |
Thinking Prompt
Before handling an error:
- What kind of failure is this?
- Expected → Result<T, E>
- Absence normal → Option<T>
- Bug/invariant → panic!
- Unrecoverable → panic!
- Who handles this?
- Caller → propagate with ?
- Current function → match/if-let
- User → friendly error message
- Programmer → panic with message
- What context is needed?
- Type of error → thiserror variants
- Call chain → anyhow::Context
- Debug info → anyhow or tracing
Trace Up ↑
When error strategy is unclear:
"Should I return Result or Option?"
↑ Ask: Is absence/failure normal or exceptional?
↑ Check: m09-domain (what does domain say?)
↑ Check: domain-* (error handling requirements)| Situation | Trace To | Question |
|---|---|---|
| Too many unwraps | m09-domain | Is the data model right? |
| Error context design | m13-domain-error | What recovery is needed? |
| Library vs app errors | m11-ecosystem | Who are the consumers? |
Trace Down ↓
From design to implementation:
"Expected failure, library code"
↓ Use: thiserror for typed errors
"Expected failure, application code"
↓ Use: anyhow for ergonomic errors
"Absence is normal (find, get, lookup)"
↓ Use: Option<T>
"Bug or invariant violation"
↓ Use: panic!, assert!, unreachable!
"Need to propagate with context"
↓ Use: .context("what was happening")Quick Reference
| Pattern | When | Example |
|---|---|---|
Result<T, E> | Recoverable error | fn read() -> Result<String, io::Error> |
Option<T> | Absence is normal | fn find() -> Option<&Item> |
? | Propagate error | let data = file.read()?; |
unwrap() | Dev/test only | config.get("key").unwrap() |
expect() | Invariant holds | env.get("HOME").expect("HOME set") |
panic! | Unrecoverable | panic!("critical failure") |
Library vs Application
| Context | Error Crate | Why |
|---|---|---|
| Library | thiserror | Typed errors for consumers |
| Application | anyhow | Ergonomic error handling |
| Mixed | Both | thiserror at boundaries, anyhow internally |
Decision Flowchart
Is failure expected?
├─ Yes → Is absence the only "failure"?
│ ├─ Yes → Option<T>
│ └─ No → Result<T, E>
│ ├─ Library → thiserror
│ └─ Application → anyhow
└─ No → Is it a bug?
├─ Yes → panic!, assert!
└─ No → Consider if really unrecoverable
Use ? → Need context?
├─ Yes → .context("message")
└─ No → Plain ?Common Errors
| Error | Cause | Fix |
|---|---|---|
unwrap() panic | Unhandled None/Err | Use ? or match |
| Type mismatch | Different error types | Use anyhow or From |
| Lost context | ? without context | Add .context() |
cannot use ? | Missing Result return | Return Result<(), E> |
Anti-Patterns
| Anti-Pattern | Why Bad | Better |
|---|---|---|
.unwrap() everywhere | Panics in production | .expect("reason") or ? |
| Ignore errors silently | Bugs hidden | Handle or propagate |
panic! for expected errors | Bad UX, no recovery | Result |
| Box<dyn Error> everywhere | Lost type info | thiserror |
Related Skills
| When | See |
|---|---|
| Domain error strategy | m13-domain-error |
| Crate boundaries | m11-ecosystem |
| Type-safe errors | m05-type-driven |
| Mental models | m14-mental-model |
